The atmospheric river storm that was bearing down on the Bay Area Wednesday night and Thursday morning raised concerns about mudslides, power outages and other problems. And a series of new storms headed our way this weekend means the end is not yet in sight.
The mid-week storm was the third atmospheric river storm since last Friday. Scientists said conditions are lining up for a series of additional “pineapple express” storms in the next few days that could create conditions not seen since 2017.
That year, multiple atmospheric river storms drenched California in succession, culminating with a massive one in mid-February that ended the 2012-16 drought, wrecked the spillway at Oroville Dam and caused $100 million in flood damage in downtown San Jose.
This year, two more atmospheric river storms are shaping up for Saturday and Monday in Northern California, with still more potentially coming the following week or two, said Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego, and one of the nation’s leading experts on atmospheric rivers.
“If these storms continue to come onshore for the next two or three weeks, that will end the drought,” he said.
Because soils have become saturated after steady December rains, billions of gallons of water are finally flowing into reservoirs, which remain at low levels from the drought but are starting to rise, Ralph noted. Multiple atmospheric storms in succession also could cause major flooding, an issue that state officials highlighted Wednesday.
“Three weeks ago we were talking about exceptional drought,” said Karla Nemeth, director of California’s Department of Water Resources. “And here we are now talking about the biggest series of storms we’ve seen in five years.”
Here’s what we’re seeing for the cold front coming into the area during the evening commute and into the night. This cold front will bring strong winds and intense rain. Avoid all unnecessary travel! #CAwx pic.twitter.com/XroRdhS8wT
— NWS Bay Area 🌉 (@NWSBayArea) January 4, 2023
To be sure, computer modeling that forecasts atmospheric river storms and other weather patterns is only precise about a week into the future. Beyond that, conditions can change, and forecasts are adjusted closer to the arrival date of storms.
But weather models generated by U.S. and European supercomputers are showing some of the best conditions for wet weather since California’s current drought began three years ago.
“The jet stream is straight-as-an arrow coming from Asia to the California coast,” said Jan Null, a meteorologist who owns Golden Gate Weather Services in Half Moon Bay. “It looks like an El Niño pattern. It is bringing a train of storms to us.”
Atmospheric rivers are the biggest “rivers” on Earth. Moisture-rich storms that often originate near Hawaii, they flow through the sky up to 2 miles above the ocean and carry twice the volume of water per second as the Amazon River and 25 times the volume of the Mississippi where it flows into the ocean.
On Wednesday, NOAA flew “hurricane hunter” planes into the current storm to gather data about its strength.
When high-pressure ridges off the coast block atmospheric rivers from California, diverting them to Canada or the Pacific Northwest, California can enter a drought. That happened repeatedly in the last major drought from 2012 to 2016, and for much of the past three winters. When the ridges are gone, as they are now, the storms can line up and hammer the West Coast like body blows from a prize fighter. But in moderation, they are key to the state’s water supply. In a typical year, California receives about a dozen such storms, which account for roughly 50% of its precipitation.
“The dry years vs. the wet years are basically because of too few or too many atmospheric rivers,” said Ralph, who devised a 1-5 scale for measuring atmospheric river storms, based on the amount of moisture they transport and the time they linger over land.
#GOES18 is now #GOESWest. A BIG THANKS to the SPoRT Data Production Team for transitioning our products today. We leave you with a GOES-18 animation of a bomb cyclone and impressive atmospheric river with a deep feed of moisture that extends back to Hawaii. #weather #satellites pic.twitter.com/RcvHWFSt9S
— NASA SPoRT (@NASA_SPoRT) January 4, 2023
Two “AR” storms, as they are called, doused the Bay Area Friday and Saturday. Those storms were category 1, the weakest, but category 3 farther north. Wednesday night’s storm was a category 3, accompanied by huge zone of low pressure called a “bomb cyclone.” Another AR storm this Saturday is expected to be a 2. The one Monday looks like a 4, Ralph’s team has forecast.
A series of other AR storms may continue for weeks, however, and should cause more concern, Ralph and other experts said.
“The impacts could be serious,” Ralph said. “The more of these that pile up back-to-back, the more likely reservoirs will fill up. We need to really pay attention in the next few weeks.”
Reservoirs across California remain low after three years of severe drought. The state’s largest, Shasta, near Redding, on Wednesday was 34% full — about 57% of its historical average for this date. Similarly, Oroville, in Butte County, was 39% full — about 74% of its average, and rising.
But with each storm, some reservoirs have already risen above normal levels. Folsom Reservoir, northeast of Sacramento, jumped in recent weeks to 58% full, or 144% of its historical average for this time of the year. Millerton Lake, north of Fresno, is now 77% full, or 146% of average.
Meanwhile, large storms in December have left California with the biggest New Year’s snowpack since 2011. On Wednesday, the statewide Sierra Nevada snowpack, the source of nearly one-third of California’s water, was 173% of its historical average. The Sierra acts as a giant frozen reservoir. As the snow melts in spring and summer, it sends water down rivers to refill reservoirs.
Wade Crowfoot, California’s secretary of natural resources, said with reservoirs and groundwater levels still low after three very dry years, it’s too soon to declare the drought over. Last year, a very wet December was followed by the driest January, February and March in the state’s recorded history, and the snowpack ended on April 1 at 37% of normal.
“We are still in the first half of the game,” Crowfoot said. “We’ve got major points on the board in terms of precipitation, snow and rain that will be helpful in coming dry months. But we are a long way from understanding how this wet season impacts our overall drought.”
Much of California, including San Francisco, Sacramento and Los Angeles, is under a flood watch today as an atmospheric river bombards the state with several inches of precipitation.
So what is an atmospheric river? https://t.co/z4mjIiyq0M pic.twitter.com/L4LQFiTmWt
— Inside Climate News (@insideclimate) January 4, 2023
Source: www.mercurynews.com